Much effort has been expended in recent years in impoving the performance of catalysts, reducing their cost and extending their useful life.
In a known method for preparing the catalysts, ceramic materials or high temperature-resisting aluminum-containing alloy materials, which generally include silica, ceramic compositions, natural silicious materials, alundum, silicon carbide, titania and zirconia etc., are used as catalyst supports with noble metals being used as the catalytic materials. However because noble metals are rare and expensive, the cost of the resulting catalysts are also expensive. Presently known rare earth metal catalysts are generally formed by impregnating the ceramic support structure with a solution of a mixture of rare earth metal salts, then drying and calcining the impregnated supports. In this method, the catalytic materials are not coated firmly and uniformly onto the supports in strict stoichiometric proportions, therefore, one can not obtain a predetermined level of catalytic activity. Other known methods for coating a catalytic materials onto supports comprise co-deposition, chemical plating, spray drying, metallurgical consolidation, freeze drying, and the like. However, all these methods are unsatisfactory because the catalytic activity can not be predetermined and the catalysts produced have a short useful life.